Cameras and other types of sensors have been used on vehicles to enable systems that act as driving aids, such as for safety, awareness, or comfort. For example, an adaptive cruise control system generally uses sensors to detect the proximity of another vehicle in order to adjust vehicle speed or maintain a set vehicle spacing. In another example, a lane departure warning system generally uses sensors to detect a location of a vehicle within a lane of traffic in order to provide a warning to the driver or execute an automatic correction in the event that the vehicle is straying from the lane of traffic. Automated or assisted driving systems generally use sensors to enable machine vision that is used to navigate the vehicle to a destination while avoiding obstacles and obeying traffic laws and procedures. The sensors for these types of systems are generally mounted on the vehicle at various locations and orientations so as to collect the data needed to operate the systems.
In order to operate effectively, however, data read by the sensors must be relatable to a known orientation and location on the vehicle. For example, if the sensor is not located on a portion of the body of the vehicle that is closest to an obstacle, than the distance between the sensor and the obstacle sensed by the sensor will not indicate the true proximity of the obstacle. A known location and orientation of a sensor on the body of the vehicle can be used with a sensor reading in order to determine a true distance between an obstacle and the body of the vehicle.
Thus, the accuracy and effectiveness of systems relying on sensors depends on the accuracy of the location and orientation information for the sensors on the body of the vehicle. Generally, sensors on a vehicle are mounted at known locations relative to defined points such as an axle or wheel, and are oriented relative to a “thrust line” of the vehicle. The thrust line of a vehicle extends forwardly from a point of intersection of the rear transverse axis of the rear wheels and the longitudinal center line of the vehicle at an angle to the center line. The angle that the thrust line makes with respect to the center line of the vehicle is determined by the toe of the rear wheels, and is generally relatively small; for example, as close to zero as possible.
A calibration process is customarily used in order to determine or validate the location and orientation of a sensor. Devices used for calibration generally include an alignment element such as a mirror or optical target mounted on a stand that is placed at a fixed location in front of the vehicle so that the target is within a line-of-sight of the sensor. Precise calibration requires that the alignment element is positioned and oriented accurately in front of the vehicle according to that vehicle's specific manufacturer's specifications. Each vehicle may include a multitude of different types of sensors at different locations. Further, depending on the manufacturer's specifications, the alignment element may have to be oriented accurately relative to the vehicle in up to six different degrees of freedom; e.g., distance in front of the vehicle, left-to-right centering, perpendicularity to the thrust line, height, orientation about a horizontal axis, and orientation about an axis along the thrust line.
As a result, the number and position of alignment elements needed to calibrate the sensors of different vehicles can vary drastically from manufacturer to manufacturer, and even from vehicle to vehicle. Thus, each manufacturer generally provides one or more separate calibration devices that include the alignment elements adapted to the vehicles they offer for sale. Conventionally, mechanics and service professionals that seek to cater to a wide variety of makes and models of vehicles need to obtain and use a multitude of different calibration devices, which are customarily costly, and which require significant training to operate and maintain. Therefore, reducing the number of calibration devices needed to cater to a wide variety of vehicles would be beneficial.